I would guess that since CS3 is a 32-bit application and not a 64-bit one that it would have the same memory usage limits that it would have with a 32-bit OS. The OS can’t make an application use something it was never designed to use.
Interesting read. So 32-bit apps on a 64-bit OS can use more memory. Neat. It also sounds like Photoshop will make the jump to 64-bit when and only when there are far more users using a 64-bit OS. Otherwise the 64-bit version of Photoshop will suffer because of time, man power and funding issues with getting it fully converted over and the 64-bit version is feature for feature right on with the 32-bit version of Photoshop. Makes sense.